1. Field of the Invention
The present invention relates to a machine for stacking random sized sheets delivered to it at high speed in either a steady or intermittent fashion. More particularly, the invention is directed toward improvements in stacking machines using a rotating delivery fan or spiral carrier.
2. Description of the Prior Art
Stacking machines of the rotating delivery fan or spiral carrier type are well known. These machines use a rotating member, such as a drum or a plurality of discs mounted for rotation on a common axis. The rotating member includes a plurality of arcuate-shaped, evenly spaced receiving slots designed to respectively receive and decelerate successive sheets fed at a relatively high speed. Adjacent slots are separated by sections or walls of the rotating member, and these walls are shaped to a thin edge to present a minimum edge profile. The successive sheets are fed to the rotating member by a suitable delivery or feeding mechanism, such as a system of feed belts and rollers. It is also known to at least partially enclose the rotating member with a fixed arcuate-shaped member to aid in the retention of the sheets within the respective slots of the rotating member. After a sheet has been inserted into a slot, the rotating member advances it to a stripping station where a stripping member, positioned in the space between adjacent discs or in a slot in the drum, engages the leading edge of the sheet, removes it from the rotating member, and transfers it to a conveyor belt or stacking table. Descriptions of stacking machines of the previously described type are found in U.S. Pat. No. 1,956,541, entitled DELIVERY MECHANISM FOR PRINTING MACHINES; U.S Pat. No. 3,162,439, entitled DOCUMENT STACKING DEVICES; and U.S. Pat. No. 3,355,169, entitled DEVICE FOR DISTRIBUTING WORK PIECES.
U.S. Pat. No. 3,062,537 discloses a machine for stacking sheet material in a receptacle or stacking bin. The apparatus includes a normally stationary stacking drum with means for feeding a sheet along the periphery of the drum to a predetermined position. At this position, means are provided to detect the presence of the sheet, to clamp the sheet to the drum and to initiate rotary movement of the drum, which carries the sheet to a suitable bin or receptacle. Because the rotary movement of the drum is under the control of the moving sheet, this type of device operates asynchronously and thereby eliminates the timing requirements of the stacker relative to the sheet feeding mechanisms of the prior art.
The previously described types of stacking devices are relatively slow because of the nature of the feed and extracting systems. U.S. Pat. No. 3,355,169 is directed to a device intended to increase this operating speed by providing for at least 50 percent more pockets for a given diameter stacker than is provided by a device using slotted wheels. The stacker wheel of the patent includes a disc having a plurality of circumferential closely spaced leaf springs mounted on its periphery. Each of these springs is secured at one end to the peripheral edge of the disc and extends in a generally tangential direction so that each two adjacent springs define an outwardly widening pocket for receiving a sheet for the like. Arcuate guide means, such as rollers or curved bars, are provided to coact with the leaf springs and bend the springs toward the peripheral edge of the rotating disc during part of a rotation to thereby grip the corresponding sheets. The guide means release the leaf springs shortly before they approach a discharge position in the receiving system, thus allowing the sheets to be removed from the wheel.
U.S. Pat. No. 3,912,255 relates to a paper sheet feeding and counting device of the type just described in which the springs or blades cooperate with the pivotal platform for neatly and accurately stacking the sheets. The blades are preferably formed of steel of a stiffness that permits them to flex or bend as they come into engagement with the top-most item on the pivotal platform, thereby preventing the blades from damaging or mutilating the sheet. However, sheet speed with such a device remains low--less than 100 inches per second. Speed beyond 100 inches per second is difficult to achieve because as the speed increases, so does the likelihood that the leading edge of a sheet will collide with the edge of the blade tip and be bounced back, thereby increasing the possibility that a sheet will be forced out of position and miss the stacker or be kicked backward, causing trailing sheets to pile up and jam.